Solid Electrolyte and Preparing Method Thereof

ABSTRACT

A method of preparing a solid electrolyte includes preparing a mixed powder with a sulfur powder, a phosphorus powder and a lithium powder. The sulfur in the sulfur powder, the phosphorus in the phosphorus powder, and the lithium in the lithium powder are each in an elemental form. The mixed powder is milled to obtain an amorphous powder. The method includes heat-treating the amorphous powder to form a crystallized solid electrolyte.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/813,673, filed Nov. 15, 2017, which claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2016-0152476filed on Nov. 16, 2016, the entire contents of both which areincorporated herein by their reference.

TECHNICAL FIELD

The present disclosure relates to a solid electrolyte derived from asingle element powder which is not based on compound powder and apreparing method thereof.

BACKGROUND

Today, secondary batteries have been widely used from large devices suchas a vehicle and a power storage system to small devices such as amobile phone, a camcorder, and a laptop.

As the secondary battery is widely applied, the demand for improvedsafety and high performance of the battery has been increased.

A lithium secondary battery which is one of the secondary batteries hasan advantage in that energy density is higher and a capacity per unitarea is larger than a nickel-manganese battery or a nickel-cadmiumbattery.

However, most of electrolytes used in the lithium secondary batteries inthe related art are liquid electrolytes such as organic solvents.Accordingly, safety problems such as leakage of electrolytes and therisk of fire resulting there from have been constantly raised.

As a result, recently, to increase safety, an interest inall-solid-state batteries using solid electrolytes rather than liquidelectrolytes as the electrolytes has been increased.

The solid electrolyte has higher safety than the liquid electrolyte dueto a non-combustible or flame-retardant property.

The solid electrolytes are divided into an oxide-based electrolyte and asulfide-based electrolyte. The sulfide-based solid electrolyte has highlithium-ionic conductivity compared to the oxide-based solid electrolyteand is stable in a wide voltage range and thus the sulfide-based solidelectrolyte is frequently used.

In Korean Patent Application Publication No. 10-2012-0095987, there isdisclosed a sulfide-based solid electrolyte manufactured by mixing andthen vitrifying Li₂S and P₂S₅. As such, in the related art, asulfide-based solid electrolyte was manufactured by using a compoundtype starting material. The cost of the compound type starting materialsuch as Li₂S is very high as about 5 million won/kg. Further, recently,attempts to improve the sulfide-based solid electrolyte by mixing acompound such as GeS₂ with Li₂S and P₂S₅ have been increased and thusthe cost of the material is further increased. The high material cost isa great obstacle to a large area of the battery according to the demandof a large-capacity energy storage technology.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

The present invention has been made in an effort to solve theabove-described problems associated with prior art.

An object of the present invention is to provide a method of preparing anew solid electrolyte without using a compound type powder as a startingmaterial.

Another object of the present invention is to provide a solidelectrolyte suitable for a large area of a battery and a preparingmethod thereof.

The objects of the present invention are not limited to the objectsdescribed above. The objects of the present invention will be moreapparent in the description below and implemented by means described inthe claims and a combination thereof.

The present invention includes the following configurations in order toachieve the above objects.

In one aspect, the present invention provides a solid electrolytederived from a single element including: a sulfur (S) element derivedfrom a simple substance sulfur powder; a phosphorus (P) element derivedfrom a simple substance phosphorus powder; and a lithium (Li) elementderived from a simple substance lithium powder.

In a preferred embodiment, the solid electrolyte derived from a singleelement may be expressed by Li_(2x)P_(2y)S_(x+5y) (0.65≤x≤0.85,0.15≤y≤0.35).

In another preferred embodiment, the solid electrolyte derived from asingle element may further include a nickel (Ni) element derived from asimple substance nickel powder, in which the solid electrolyte may beexpressed by Li_(a)P_(b)S_(c)Ni_(d) (12≤a≤18, 0.8≤b≤6.4, 13.2≤c≤26,1.2≤d≤9.6).

In still another preferred embodiment, the solid electrolyte derivedfrom a single element may further include a chlorine (Cl) elementderived from a lithium chloride (LiCl) powder, in which the solidelectrolyte may be expressed by Li_(a)P_(b)S_(c)Ni_(d)Cl_(e) (12≤a≤22,0.8≤b≤6.4, 13.2≤c≤26, 1.2≤d≤9.6, 1≤e≤4).

In another aspect, the present invention provides a method of preparinga solid electrolyte derived from a single element, the method including:(1) preparing a mixed powder containing a simple substance sulfurpowder, a simple substance phosphorus powder and a simple substancelithium powder; (2) milling the mixed powder to obtain an amorphouspowder; and (3) heat-treating the amorphous powder to crystallize.

In a preferred embodiment, the mixed powder in step (1) may be mixed bymeasuring the simple substance sulfur powder, the simple substancephosphorus powder and the simple substance lithium powder according to acomposition of Li_(2x)P_(2y)S_(x+5y) (0.65≤x≤0.85, 0.15≤y≤0.35).

In another preferred embodiment, the mixed powder may consist of thesimple substance sulfur powder, the simple substance phosphorus powderand the simple substance lithium powder.

In still another preferred embodiment, the amorphous powder may beobtained by milling the mixed powder under conditions of 300 RPM to 1000RPM and 4 hrs to 40 hrs by using a planetary mill.

In yet another preferred embodiment, step (2) may be a step of mixing 1wt % to 50 wt % of the mixed powder and 50 wt % to 99 wt % of a solventand then wet-milling the mixture.

In still yet another preferred embodiment, the solvent may be any oneselected from a group consisting of at least one hydrocarbon-basedsolvent of pentane, hexane, 2-ethyl hexane, heptane, octane,cyclohexane, and methyl cylcohexane; at least one BTX-based solvent ofbenzene, toluene, xylene, and ethylbenzene; at least one ether-basedsolvent of diethyl ether, tetrahydrofuran and 1,4-dioxane; and at leastone ester-based solvent of ethyl propionate and propyl propionate or amixed solvent thereof.

In a further preferred embodiment, the crystallizing in step (3) may beperformed by heat-treating the amorphous powder at 200° C. to 500° C.and 1 min to 100 hrs.

In another further preferred embodiment, steps (1) to (3) may beperformed in a dry room.

In still another further preferred embodiment, in step (1), a simplesubstance nickel powder may be further mixed with the mixed powder, andthe simple substance sulfur powder, the simple substance phosphoruspowder, the simple substance lithium powder and the simple substancenickel powder may be measured according to a composition ofLi_(a)P_(b)S_(c)Ni_(d) (12≤a≤16, 0.8≤b≤6.4, 13.2≤c≤23.6, 1.2≤d≤9.6) andmixed. In yet another further preferred embodiment, in step (1), asimple substance nickel powder and a lithium chloride powder may befurther mixed with the mixed powder, and the simple substance sulfurpowder, the simple substance phosphorus powder, the simple substancelithium powder, the simple substance nickel powder and the lithiumchloride powder may be measured according to a composition ofLi_(a)P_(b)S_(c)Ni_(d)Cl_(e)(12≤a≤20, 0.8≤b≤6.4, 13.2≤c≤23.6, 1.2≤d≤9.6,1≤e≤4) and mixed.

In still yet another aspect, the present invention provides an allsolid-state battery including a positive electrode, a negativeelectrode, and a solid electrolyte layer interposed between the positiveelectrode and the negative electrode, in which at least one of thepositive electrode, the negative electrode, and the solid electrolytelayer includes the solid electrolyte derived from the single element.

According to the present invention, a solid electrolyte havinglithium-ionic conductivity and discharge capacity when applying abattery which are equal to or higher than those in the related art canbe manufactured at costs of less than about 5% compared with the relatedart. Accordingly, the solid electrolyte according to the presentinvention can largely contribute to a large area of an all solid-statebattery.

As the solid electrolyte derived from the single element, thecomposition can be easily changed and induction for development ofvarious solid electrolytes having different ratios of elements oflithium, phosphorus, sulfur, and the like can be provided.

The solid electrolyte can be prepared safely and cheaply because aseparate device such as a glove box is not required.

The effects of the present invention are not limited to theaforementioned effects. It should be understood that the effects of thepresent invention include all effects inferable from the descriptionbelow.

Other aspects and preferred embodiments of the invention are discussedinfra.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

The above and other features of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of thepresent invention, and wherein:

FIG. 1 schematically illustrates a method of preparing a solidelectrolyte according to the present invention;

FIG. 2 is a scanning electron microscope (SEM) measurement result for asolid electrolyte in Examples 1 to 3. FIG. 2A is a result for Example 1,FIG. 2B is a result for Example 2, and FIG. 2C is a result for Example3;

FIG. 3 is an X-ray diffraction spectroscopy (XRD) result for the solidelectrolyte in Examples 1 to 3;

FIG. 4 is an SEM measurement result for a solid electrolyte in Example4;

FIG. 5 is an SEM measurement result for a solid electrolyte in Example5;

FIG. 6 is a result of measuring a current when predetermined voltage isapplied to the solid electrolyte in Examples 1 and 4;

FIG. 7 is a result of measuring a discharge capacity of an allsolid-state battery to which the solid electrolyte is applied in Example1;

FIG. 8 is a result of measuring a discharge capacity of an allsolid-state battery to which the solid electrolyte is applied in Example4; and

FIG. 9 is a result of measuring a discharge capacity of an allsolid-state battery to which the solid electrolyte is applied in Example5.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Hereinafter reference will now be made in detail to various embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings and described below. While the invention will bedescribed in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention to those exemplary embodiments. On the contrary, the inventionis intended to cover not only the exemplary embodiments, but alsovarious alternatives, modifications, equivalents and other embodiments,which may be included within the spirit and scope of the invention asdefined by the appended claims.

Hereinafter, the present invention will be described in detail throughexemplary embodiments. The exemplary embodiments of the presentinvention may be modified in various forms as long as the gist of theinvention is not changed. However, the scope of the present invention isnot limited to the following exemplary embodiments.

When it is determined that the description for the known configurationsand functions may obscure the gist of the present invention, thedescription for the known configurations and functions will be omitted.In this specification, the term “comprise” means that other constituentelements may be further included unless otherwise listed.

A solid electrolyte derived from a single element according to thepresent invention may include a sulfur (S) element derived from a simplesubstance sulfur powder, a phosphorus (P) element derived from a simplesubstance phosphorus powder and a lithium (Li) element derived from asimple substance lithium powder.

As illustrated in FIG. 1, the solid electrolyte derived from the singleelement may be prepared by (1) preparing a mixed powder containing asimple substance sulfur powder, a simple substance phosphorus powder andsimple substance lithium powder (S1), (2) milling and amorphizing themixed powder (S2), and (3) heat-treating and crystallizing theamorphized mixed powder (S3).

In this specification, the ‘simple substance’ means a single elementmaterial constituted by a single element to have a unique chemicalproperty. Accordingly, the simple substance sulfur powder means a powderstate of the simple substance sulfur which is constituted by only thesulfur (S) element to have a unique chemical property, the simplesubstance phosphorus powder means a powder state of the simple substancephosphorus which is constituted by only the phosphorus (P) element tohave a unique chemical property, and the simple substance lithium powdermeans a powder state of the simple substance lithium which isconstituted by only the lithium (Li) element to have a unique chemicalproperty.

In the related art, in order to manufacture the sulfide-based solidelectrolyte such as Li₃PS₄, a starting material in which Li₂S and P₂S₅are mixed at a mole % ratio of 75:25 was used. In the related art, inthe case of using a compound type starting material, material cost isvery high. In the case of the starting material (75Li₂S-25P₂S₅), thematerial cost reaches about 5 million won/kg (approximatelyUSD$4500/Kg). Further, since Li₂S is vulnerable to moisture and P₂S₅ isa compound that has a high risk of explosion in air, the materials needto be handled in a separate glove box.

Embodiments of the present invention are contrived to solve the aboveproblems and constraints and have a technical feature that the solidelectrolyte is prepared from the starting material mixed by measuringthe simple substance sulfur powder, the simple substance phosphoruspowder, and the simple substance lithium powder according to thecomposition of the desired solid electrolyte.

In various embodiments of the present invention, since the simplesubstance sulfur powder, the simple substance phosphorus powder, thesimple substance lithium powder, and the like are used as the startingmaterial, the material cost is about 150,000 won/kg (approximatelyUSD$135/Kg) and thus the solid electrolyte may be prepared atsignificantly low cost compared to the case of using the compound typepowder. That is, embodiments of the present invention have a technicalsignificance in that it is verified that when the solid electrolyte isprepared by amorphizing and crystallizing the mixed powder, the solidelectrolyte having excellent lithium ion conductivity, dischargingcapacity when applied to the battery, and the like can be obtained atlow cost.

Embodiments of the present invention have advantages of preparing thesolid electrolyte safely and easily without requiring a separate devicesuch as a glove box because a compound type starting material which isharmful to the human body, vulnerable to moisture, or has the risk ofexplosion is not used.

In particular, step (1) is a step of preparing the mixed powdercontaining the simple substance sulfur powder, the simple substancephosphorus powder, and the simple substance lithium powder.

The simple substance lithium powder may be replaced with a singlematerial containing a lithium metal. The single material may correspondto any material which may be mixed and amorphized with the simplesubstance sulfur powder, the simple substance phosphorus powder, and thelike by milling and the like, not the compound type, and for example,lithium foil and the like.

According to an exemplary embodiment of the present invention, step (1)may be a step of preparing a mixed powder by measuring and mixing thesimple substance sulfur powder, the simple substance phosphorus powder,and the simple substance lithium powder according to a composition ofLi_(2x)P_(2y)S_(x+5y) (0.65≤x≤0.85, 0.15≤y≤0.35) which is a desiredsolid electrolyte.

Step (2) may be a step of milling and amorphizing the mixed powder.Particularly, the amorphizing may be milling the mixed powder underconditions of 300 RPM to 1,000 RPM and 4 hrs to 40 hrs by using aplanetary mill.

The amorphizing may be performed by wet milling or dry milling andpreferably performed by wet milling for uniform formation of the crystalwhen the crystallization is performed through heat-treating.

The wet milling may be wet milling by mixing 1 wt % to 50 wt % of themixed powder and 50 wt % to 99 wt % of the solvent, preferably 4 wt % to20 wt % of the mixed powder and 80 wt % to 96 wt % of the solvent, andmore preferably 5 wt % to 15 wt % of the mixed powder and 75 wt % to 95wt % of the solvent. When the mixed powder is less than 1 wt %, theyield is too low and thus it may not be suitable for mass production,and when the mixed powder is more than 50 wt %, it may be difficult toobtain a uniformly amorphized material like dry milling.

The solvent may be any one selected from a group consisting of at leastone hydrocarbon-based solvent of pentane, hexane, 2-ethyl hexane,heptane, octane, cyclohexane, and methyl cyclohexane; at least oneBTX-based solvent of benzene, toluene, xylene, and ethylbenzene; atleast one ether-based solvent of diethyl ether, tetrahydrofuran and1,4-dioxane; and at least one ester-based solvent of ethyl propionateand propyl propionate, or a mixed solvent thereof. However, inembodiments of the present invention, the solvent is not limited theretoand it is understood that the solvent includes all solvents which aremainly used for wet milling through a planetary mill.

Step (3) may be a step of heat-treating and crystallizing the amorphizedmixed powder through milling. In detail, the crystallization may beheat-treating the mixed powder under conditions of 200° C. to 500° C.and 1 min to 100 hrs.

In the case of amorphizing the mixed powder through wet milling in step(2), a drying step before performing step (3) may be further performed.The dry step is to remove the remaining solvent in the milled mixedpowder and may be vacuum drying, heat drying, or vacuum and heat dryingunder conditions of room temperature to 200° C. and 1 min to 10 hrs.

The preparing method of the solid electrolyte derived from the singleelement according to the present invention does not need to be performedin the glove box because the mixed powder is used as the startingmaterial. Accordingly, steps (1) to (3) may be performed in a dry room.

According to another exemplary embodiment of the present invention, instep (1), the simple substance nickel powder is further mixed with themixed powder to obtain a solid electrolyte further containing a nickel(Ni) element derived from the simple substance nickel powder.

Particularly, steps (2) and (3) are performed by using the mixed powder,as the starting material, mixed by measuring the simple substance sulfurpowder, the simple substance phosphorus powder, the simple substancelithium powder and the simple substance nickel powder in step (1)according to a composition of Li_(a)P_(b)S_(c)Ni_(d) (12≤a≤18,0.8≤b≤6.4, 13.2≤c≤26, 1.2≤d≤9.6) as a desired solid electrolyte,respectively, to prepare the solid electrolyte containing the nickelelement.

According to yet another exemplary embodiment of the present invention,the simple substance nickel powder and a lithium chloride (LiCl) powderare further mixed in the mixed powder in step (1) to obtain the solidelectrolyte containing a nickel (Ni) element derived from the simplesubstance nickel powder and a chlorine (Cl) element derived from thelithium chloride powder.

Particularly, steps (2) and (3) are performed by using the mixed powder,as the starting material, mixed by measuring the simple substance sulfurpowder, the simple substance phosphorus powder, the simple substancelithium powder, the simple substance nickel powder and the lithiumchloride powder in step (1) according to a composition ofLi_(a)P_(b)S_(c)Ni_(d)Cl_(e)(12≤a≤22, 0.8≤b≤6.4, 13.2≤c≤26, 1.2≤d≤9.6,1≤e≤4) as a desired solid electrolyte, respectively, to prepare thesolid electrolyte containing the nickel element and the chlorideelement.

As such, the present invention has an advantage in that the compositionof the solid electrolyte is easily changed, removed, and added by usingthe simple substance phosphorus material, not the compound type materialas the starting material. Accordingly, the present invention can alsoprovide induction in the development of solid electrolytes havingvarious compositions.

Hereinafter, the present invention will be described in more detailthrough detailed Examples and Test Examples. However, these Examples andTest Examples are to exemplify the present invention and the scope ofthe present invention is not limited thereto.

Examples

The following examples illustrate the invention and are not intended tolimit the same.

(Example 1) In order to prepare a solid electrolyte represented byLi₃PS₄(75Li₂S-25P₂S₅), the following steps were performed. A simplesubstance sulfur powder (Sigma Aldrich Corporation, sulfur), a simplesubstance phosphorus powder (Sigma Aldrich Corporation, phosphorous),and a simple substance lithium powder (FMC Corporation, lithium powder)were used as a starting material. 7.12 g of the simple substance sulfurpowder, 1.72 g of the simple substance phosphorus powder, and 1.16 g ofthe simple substance lithium powder were measured and mixed to have thesame composition ratio (mole ratio) as 75Li₂S-25P₂S₅ to prepare a mixedpowder. 82.5 g of xylene was mixed with the mixed powder and then putinto a planetary ball mill container together with 575 g of zirconiaballs. The mixed powder was milled and amorphized at about 360 RPM.Thereafter, the obtained mixed powder was vacuum-dried for 2 hrs atabout 160° C. to remove the remaining xylene. Next, the mixed powder washeat-treated for 2 hrs at 230° C. and crystallized to obtain the solidelectrolyte.

(Example 2) Except for using lithium foil (HONJO METAL Corporation,purity 99.9%) instead of the simple substance lithium powder as astarting material, a solid electrolyte was prepared by the same materialand method as Example 1.

(Example 3) In order to prepare a solid electrolyte represented byLi₃PS₄(75Li₂S-25P₂S₅), the following steps were performed. A simplesubstance sulfur powder (Sigma Aldrich Corporation, sulfur), a simplesubstance phosphorus powder (Sigma Aldrich Corporation, phosphorous),and lithium foil (HONJO METAL Corporation, purity 99.9%) were used as astarting material. 7.12 g of the simple substance sulfur powder, 1.72 gof the simple substance phosphorus powder, and 1.16 g of the lithiumfoil were measured and mixed to have the same composition ratio (moleratio) as 75Li₂S-25P₂S₅ to prepare a mixed powder. The mixed powder wasput into a planetary ball mill container together with 300 g of zirconiaballs. The mixed powder was milled and amorphized at about 360 RPM.Next, the mixed powder was heat-treated for 2 hrs at 230° C. andcrystallized to obtain the solid electrolyte.

FIG. 2 is a scanning electron microscope (SEM) measurement result for asolid electrolyte in Examples 1 to 3. FIG. 2A is a result for Example 1,FIG. 2B is a result for Example 2, and FIG. 2C is a result for Example3.

It can be seen that the crystal of the solid electrolyte in Example 1(the simple substance lithium powder and wet milling) is uniformlyformed and it can be verified that in Example 2 (lithium foil and wetmilling) and Example 3 (lithium foil and dry milling), the formation ofcrystals is slightly uneven.

This can be seen from an X-ray diffraction spectroscopy (XRD) result forthe solid electrolyte in Examples 1 to 3 in FIG. 3. It can be verifiedthat the solid electrolyte in Example 1 has substantially the same peakas Li₃PS₄ which is a similar phase as THIO-LISICON III, whereas in thesolid electrolytes in Examples 2 and 3, the peaks are clearly separatedand not measured and thus the growth and the uniformity of the crystalsslightly deteriorate.

Accordingly, in the preparation of the solid electrolyte according tothe present invention, like Example 1, the mixed powder may be preparedby using a simple substance lithium powder as a starting material andamorphized by wet milling and then crystallized.

(Example 4) In order to prepare a solid electrolyte represented byLi₁₆P₄S₂₀Ni₃(8Li₂S-2P₂S₅-1Ni₃S₂), the following steps were performed. Asa starting material, a simple substance sulfur powder, a simplesubstance phosphorus powder, a simple substance lithium powder and asimple substance nickel powder were used. 6.09 g of the simple substancesulfur powder, 1.18 g of the simple substance phosphorus powder, 1.06 gof the simple substance lithium powder, and 1.67 g of the simplesubstance nickel powder were measured and mixed to have the samecomposition ratio (mole ratio) as 8Li₂S-2P₂S₅-1Ni₃S₂ to prepare a mixedpowder. 82.5 g of xylene was mixed with the mixed powder and then putinto a planetary ball mill container together with 575 g of zirconiaballs. The mixed powder was milled and amorphized at about 360 RPM.Thereafter, the obtained mixed powder was vacuum-dried for 2 hrs atabout 160° C. to remove the remaining xylene. Next, the mixed powder washeat-treated for 2 hrs at 260° C. and crystallized to obtain the solidelectrolyte.

(Example 5) In order to prepare a solid electrolyte represented byLi₂₀P₄S₂₀Ni₃Cl₄(8Li₂S-2P₂S₅-1Ni₃S₂-4LiCl), the following steps wereperformed. As a starting material, a simple substance sulfur powder, asimple substance phosphorus powder, a simple substance lithium powder, asimple substance nickel powder and a lithium chloride powder were used.5.25 g of the simple substance sulfur powder, 1.01 g of the simplesubstance phosphorus powder, 0.91 g of the simple substance lithiumpowder, 1.44 g of the simple substance nickel powder, and 1.39 g of thelithium chloride powder were measured and mixed to have the samecomposition ratio (mole ratio) as 8Li₂S-2P₂S₅-1Ni₃S₂-4LiCl to prepare amixed powder. 82.5 g of xylene was mixed with the mixed powder and thenput into a planetary ball mill container together with 575 g of zirconiaballs. The mixed powder was milled and amorphized at about 360 RPM.Thereafter, the obtained mixed powder was vacuum-dried for 2 hrs atabout 160° C. to remove the remaining xylene. Next, the mixed powder washeat-treated for 2 hrs at 26° C. and crystallized to obtain the solidelectrolyte.

FIG. 4 is an SEM measurement result for a solid electrolyte in Example 4and FIG. 5 is an SEM measurement result for a solid electrolyte inExample 5. In Examples 4 and 5, like Example 1, it can be seen that thesimple substance lithium powder is used as the starting material andamorphized by wet milling and then crystallized, and thus the crystalsare uniformly formed.

Hereinafter, for convenience of description, the solid electrolytes inExamples 1, 4, and 5 are referred to as LSPS, LNPS and LNPS-Cl,respectively, and called according to a kind of element included in eachsolid electrolyte.

Test Examples

(Test Example 1) Lithium-ionic conductivities of solid electrolytes inExample 1 (LSPS), Example 4 (LNPS) and Example 5 (LNPS-Cl) weremeasured. LSPS, LNPS and LNPS-Cl were compressively molded to form amolding body for measurement (with a diameter of 13 mm and a thicknessof 0.6 mm). An AC potential of 10 mV was applied to the molding body andthen an impedance value was measured by performing a frequency sweepingof 1×10⁶ to 100 Hz to see lithium-ion conductivity.

As a result, the lithium-ionic conductivities of 1.0×10⁻⁴ S/cm of theLSPS in Example 1, 1.4×10⁻⁴ S/cm of the LNPS in Example 4, and 1.4×10⁻³S/cm of the LNPS-Cl in Example 5 were shown.

(Test Example 2) The lithium ion transport number of the solidelectrolytes according to Example 1 (LSPS) and Example 4 (LNPS) wasmeasured. LSPS and LNPS were compressively molded to form a molding bodyfor measurement (with a diameter of 13 mm and a thickness of 0.6 mm).Then, a current was measured by applying 1V. The result is illustratedin FIG. 6.

Resistance values R of the LSPS and the LNPS were calculated throughFIG. 6 and the Ohm's law (V=IR). Electronic conductivity (1/R×t/A) wascalculated from the resistance value R, a cross-sectional area A of themolding body for measurement, and a thickness t of the molding body formeasurement. The electronic conductivity of the LSPS was calculated as1.94×10⁻⁹ S/cm, and the electronic conductivity of the LNPS wascalculated as 1.88×10⁻⁹ S/cm. Next, the lithium ion transport number(σ_(i)/(σ_(e)+σ_(i)), σ_(i) is conductivity of lithium ions and σ_(e) isconductivity of electrons) was calculated from the electronicconductivity.

As a result, the lithium ion transport number of the LSPS was calculatedas 0.9999981 and the lithium ion transport number of the LNPS wascalculated as 0.9999963 to be very close to 1.

Referring to the results of Test Examples 1 and 2, it can be seen thatthe solid electrolyte prepared according to the present inventioncontributes to improvement of the characteristic of the all solid-statebattery because the lithium-ionic conductivity is 10⁻⁴ S/cm or more andthe lithium ion transport number is approximately 1.

(Test Example 3) An all solid-state battery was manufactured by applyingsolid electrolytes in Example 1 (LSPS), Example 4 (LNPS) and Example 5(LNPS-Cl) to solid electrolyte layers and a discharge capacity wasmeasured. The all solid-state battery was constituted by a positiveelectrode, a negative electrode, and a solid electrolyte layerinterposed between the positive electrode and the negative electrode.The solid electrolyte layer was formed with a thickness of 500 μm bycompressively molding the LSPS, the LNPS, and the LNPS-Cl, and as thepositive electrode, a powder containing an active material (Nb-coatedNCM622), a solid electrolyte (a solid electrolyte used in the solidelectrolyte layer), and a conductive material (Super C) was formed onthe solid electrolyte layer with an active material loading amount of5.8 mg/cm² and a thickness of 30 μm, and as the negative electrode,indium foil with a thickness of 100 μm was used.

With respect to the all solid-state battery, a discharge capacity wasmeasured by performing charging and discharging under a constant current(CC) condition in a range of 2 V to 3.58 V at rate limiting of 0.02 Crate.

FIG. 7 is a result of measuring a discharge capacity of an allsolid-state battery to which the solid electrolyte (LSPS) of Example 1is applied. It can be seen that when the LSPS is applied to the solidelectrolyte layer, a discharge capacity of about 140 mAh/g may beimplemented.

FIG. 8 is a result of measuring a discharge capacity of an allsolid-state battery to which the solid electrolyte (LNPS) of Example 4is applied. It can be seen that when the LNPS is applied to the solidelectrolyte layer, a discharge capacity of about 110.3 mAh/g may beimplemented.

FIG. 9 is a result of measuring a discharge capacity of an allsolid-state battery to which the solid electrolyte (LNPS-Cl) of Example5 is applied. It can be seen that when the LNPS-Cl is applied to thesolid electrolyte layer, a discharge capacity of about 111.7 mAh/g maybe implemented.

According to the solid electrolyte derived from the single element andthe preparing method thereof according to the present invention throughTest Examples 1 to 3, it can be seen that the solid electrolyte capableof implementing equivalent or higher lithium-ionic conductivity and adischarge capacity can be obtained at much lower material costs than therelated art.

Accordingly, embodiments of the present disclosure describe a solidelectrolyte derived from single element powders and not based oncompound powders.

The present invention proposes a new paradigm for the solid electrolyteand the preparing method thereof beyond the old framework in the relatedart. Therefore, it will be apparent to those skilled in the art thatclues capable of overcoming the limitations of mass production and alarge area of the all solid-state battery can be obtained from thepresent invention.

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the invention, the scope of which isdefined in the appended claims and their equivalents.

What is claimed is:
 1. A solid electrolyte derived from a singleelement, comprising: a sulfur (S) element derived from a simplesubstance sulfur powder; a phosphorus (P) element derived from a simplesubstance phosphorus powder; and a lithium (Li) element derived from asimple substance lithium powder.
 2. The solid electrolyte of claim 1,wherein the solid electrolyte is Li_(2x)P_(2y)S_(x+5y) (0.65≤x≤0.85,0.15≤y≤0.35).
 3. The solid electrolyte of claim 1, further comprising: anickel (Ni) element derived from a simple substance nickel powder. 4.The solid electrolyte of claim 3, wherein the solid electrolyte isLi_(a)P_(b)S_(c)Ni_(d) (12≤a≤18, 0.8≤b≤6.4, 13.2≤c≤26, 1.2≤d≤9.6). 5.The solid electrolyte of claim 3, further comprising: a chlorine (Cl)element derived from a lithium chloride(LiCl) powder.
 6. The solidelectrolyte of claim 5, wherein the solid electrolyte isLi_(a)P_(b)S_(c)Ni_(d)Cl_(e) (12≤a≤22, 0.8≤b≤6.4, 13.2≤c≤26, 1.2≤d≤9.6,1≤e≤4).
 7. A method of preparing a solid electrolyte, the methodcomprising: preparing a mixed powder comprising a sulfur powder, aphosphorus powder and a lithium powder, wherein the sulfur in the sulfurpowder, the phosphorus in the phosphorus powder, and the lithium in thelithium powder are each in an elemental form; milling the mixed powderto obtain an amorphous powder; and heat-treating the amorphous powder toform a crystallized solid electrolyte.
 8. The method of claim 7, whereinpreparing the mixed powder comprises mixing the sulfur powder, thephosphorus powder and the lithium powder according to a composition ofLi_(2x)P_(2y)S_(x+5y) (0.65≤x≤0.85, 0.15≤y≤0.35).
 9. The method of claim7, wherein the mixed powder consists of the sulfur powder, thephosphorus powder, and the lithium powder.
 10. The method of claim 7,wherein the amorphous powder is obtained by milling the mixed powderunder conditions of 300 RPM to 1000 RPM and 4 hrs to 40 hrs by using aplanetary mill.
 11. The method of claim 7, wherein the millingcomprises: forming a slurry by mixing a 1 wt % to 50 wt % of the mixedpowder with 50 wt % to 99 wt % of a solvent and then wet milling theslurry to obtain the amorphous powder, wherein heat-treating theamorphous powder comprises heat-treating the wet milled slurry.
 12. Themethod of claim 11, wherein the solvent is at least one selected from agroup consisting of: at least one hydrocarbon-based solvent of pentane,hexane, 2-ethyl hexane, heptane, octane, cyclohexane, and methylcyclohexane; at least one BTX-based solvent of benzene, toluene, xylene,and ethylbenzene; at least one ether-based solvent of diethyl ether,tetrahydrofuran, and 1,4-dioxane; at least one ester-based solvent ofethyl propionate, and propyl propionate; or a mixture thereof.
 13. Themethod of claim 7, wherein the milling comprises dry milling.
 14. Themethod of claim 7, wherein the heat-treating comprises heat-treating theamorphous powder at 200° C. to 500° C. and 1 min to 100 hrs.
 15. Themethod of claim 7, wherein the preparing, the milling, and theheat-treating are performed in a dry room.
 16. The method of claim 7,wherein the preparing comprises: mixing a nickel powder and a lithiumchloride powder with the mixed powder, wherein the sulfur powder, thephosphorus powder, the lithium powder, the nickel powder, the lithiumchloride powder are mixed according to a composition ofLi_(a)P_(b)S_(c)Ni_(d)Cl_(e) (12≤a≤22, 0.8≤b≤6.4, 13.2≤c≤26, 1.2≤d≤9.6,1≤e≤4), and the nickel in the nickel powder and the chloride in thelithium chloride powder are each in an elemental form.
 17. An allsolid-state battery comprising: a positive electrode, a negativeelectrode, and a solid electrolyte layer interposed between the positiveelectrode and the negative electrode, wherein at least one of thepositive electrode, the negative electrode, and the solid electrolytelayer includes the solid electrolyte of claim
 1. 18. A method ofpreparing a solid electrolyte, the method comprising: preparing a mixedpowder comprising a sulfur powder, a phosphorus powder and a lithiumpowder, wherein the sulfur in the sulfur powder, the phosphorus in thephosphorus powder, and the lithium in the lithium powder are each in anelemental form; adding the mixed powder in to a solvent; wet milling themixed powder in the solvent, wherein the wet milling amorphizes themixed powder in the solvent; and heat-treating the amorphized mixedpowder in the solvent, wherein the heat-treating removes the solvent andcrystallizes the amorphized mixed powder to form the solid electrolyte.19. The method of claim 18, wherein preparing the mixed powder comprisesmixing the sulfur powder, the phosphorus powder and the lithium powderaccording to a composition of Li_(2x)P_(2y)S_(x+5y) (0.65≤x≤0.85,0.15≤y≤0.35).
 20. The method of claim 18, wherein the mixed powderconsists of the sulfur powder, the phosphorus powder, and the lithiumpowder.
 21. The method of claim 18, wherein the wet milling comprisesmilling the mixed powder under conditions of 300 RPM to 1000 RPM and 4hrs to 40 hrs by using a planetary mill.
 22. The method of claim 18,wherein adding the mixed powder in to the solvent comprises: mixing a 1wt % to 50 wt % of the mixed powder with 50 wt % to 99 wt % of thesolvent.
 23. The method of claim 18, wherein the solvent is a solventselected from a group consisting of: a hydrocarbon-based solvent ofpentane, hexane, 2-ethyl hexane, heptane, octane, cyclohexane, or methylcyclohexane; a BTX-based solvent of benzene, toluene, xylene, orethylbenzene; an ether-based solvent of diethyl ether, tetrahydrofuran,or 1,4-dioxane; and an ester-based solvent of ethyl propionate, orpropyl propionate.
 24. The method of claim 18, wherein the heat-treatingcomprises heat-treating at 200° C. to 500° C. and 1 min to 100 hrs. 25.The method of claim 18, wherein the preparing, the adding, the wetmilling, and the heat-treating are performed in a dry room.
 26. Themethod of claim 18, wherein the preparing comprises: mixing a nickelpowder and a lithium chloride powder with the mixed powder, wherein thesulfur powder, the phosphorus powder, the lithium powder, the nickelpowder, the lithium chloride powder are mixed according to a compositionof Li_(a)P_(b)S_(c)Ni_(d)Cl_(e) (12≤a≤22, 0.8≤b≤6.4, 13.2≤c≤26,1.2≤d≤9.6, 1≤e≤4), and the nickel in the nickel powder and the chloridein the lithium chloride powder are each in an elemental form.